The prior art discloses a molten metal transfer pump (see patent RU 68077, IPC F04D 7/00, F04D7/06, F04D29/00, F04D29/04, issued on Nov. 10, 2007), comprising a case, an impeller, mounted on the shaft, connected to the drive and enclosed in the case by means of the upper and lower bearings, with the lower journal plain bearing made of structural ceramics resistant to thermal and corrosion effect of molten metal, more specifically, of self-bonded silicon carbide or silicone nitride, or oxide ceramics based on the aluminum oxide.
The prior art pump has a longer operational life of the wet end under conditions of thermal and corrosion effect of molten metal; however, technologically it is extremely difficult to manufacture the lower journal plain bearing of structural ceramics.
The prior art discloses a molten metal transfer pump (see U.S. Pat. No. 4,475,866, IPC F01D 25/14; F04D 7/00; F04D 7/06, F04D 29/04; F04D 29/047, issued on Oct. 9, 1984) which includes a cylindrical case, drive-connected shaft, located vertically along the axis of the case, and hydrostatic plain bearing supporting the lower part of the shaft together with the impeller. The plain bearing includes a rotor part in the form of cylindrical clutch mounted on the shaft, and stator part in the form of cylindrical bushing with radial holes meant for supply of molten metal to the sliding surfaces of the bearing. The rotor and stator parts of the bearing are made of stainless steel while their sliding surfaces are made of stellite (cobalt-chromium-tungsten alloy).
Disadvantage of this prior art pump is the possibility of tearing of mating surfaces at pump operation during nonsteady-state modes.
The prior art discloses a molten metal transfer pump (see U.S. Pat. No. 5,685,701, IPC F04D29/04, F04D7/00, F04D7/06, issued on Nov. 11, 1997), comprising a pump chamber, drive-connected shaft made of fire-proof material including graphite with radial bearing surface, and a bucket wheel, fixed on the shaft end. The shaft is installed in the pump chamber using the upper and lower bearings. The lower journal plain bearing is made in the form of two silicon carbide rings having a rectangular cross section and enclosed in the case. The pump is meant for transfer of liquid zinc and aluminum.
Disadvantage of this prior art pump is the complexity of manufacturing of mating rings of silicon carbide.
The prior art discloses a molten metal transfer pump (see patent RU 73924, IPC F04D 1/00, IPC F04D 3/00, issued on Jun. 10, 2008), comprising a case, in which a shaft with a mounted impeller is installed on the upper rolling bearing, located above the level of liquid metal, and on the lower plain bearing, located under the level of liquid metal. The lower plain bearing is made in the form of two successively mounted bushings (separated by a chamber) of the shaft with curved channels on their cylindrical surfaces forming a labyrinth screw pump. Direction of swirl of the channels of one surface of the shaft bushing is the same as the direction of shaft rotation, and direction of the channels of the other surface is opposite to it. Shaft bushings are interconnected with two successively mounted bearing bushings installed in the case in axial alignment with the shaft. Bearing bushings are fitted with curved channels located on their inner cylindrical surface with the direction of swirl opposite to the direction of swirl of the channels on the mating opposite surfaces of shaft bushings.
Disadvantage of this prior art pump is the complexity of manufacturing of shaft bushings and bearing bushings with curved channels on the surface, as well as the wear of helical surfaces between the channels of shaft and bearing bushings in case of misalignment between the axes of the upper bearing and lower plain bearing.
The prior art discloses a molten metal transfer pump (see application US 2013068412, IPC B22D 23/00, B22D 39/02, F04D 3/00, issued on Mar. 21, 2013), congruent with the claimed solution in the most of essential features and taken as a prototype. The prior art prototype pump comprises a case, impeller, mounted on the shaft, connected to the drive and enclosed in the case by means of the upper and lower bearings. The lower journal plain bearing is comprised of stator and rotor parts. The stator part of the lower journal plain bearing is made in the form of two bushings spaced along the axis of the shaft and installed in the case in axial alignment with the shaft; the rotor part of the lower journal plain bearing is made in the form of two shaft-mounted bushings lying opposite to the bushings of the stator part. The bushings of the stator and rotor parts of the lower journal bearing are made of silicon carbide based ceramics.
Disadvantage of this prior art pump is the complexity of manufacturing of mating bushings of silicon carbide based ceramics, as well as the possibility of tearing of material of bushings made of silicon carbide based ceramics at pump startup and its operation at low speed.